Official editorial

Problems on Codeforces are generally harder than ordinary interview problems. If your goal is only interviews, practicing LeetCode is enough. But if you are interested in algorithms and competitive programming, I strongly encourage you to give it a try. The quantity and quality of the problems far exceed LeetCode. It also provides different tracks for students at different levels, with different problem difficulties. For high-level players, the contest experience is much better.

So far I have participated in two Div.2 contests, and my rating is 1480. Yes, the initial rating is 1500, and I actually dropped.

Today was another speed contest. Python tells us, “Life is short; I use Python.” I implemented two problems in Python, problems 1 and 4. In fact, for problem 3, directly calling Python’s Str API would have been even smoother, but at the time I chose to implement it with Trie + automaton, so it was only fair that my ranking dropped.

1408. String Matching in an Array

Not difficult; a speed contest. I found that in many speed contests, the third problem is sometimes even harder than the fourth.

1399. Count Largest Group

This week was another speed contest, and a full 800 people got AK. Maybe because of the pandemic, programmers are all WFH (work from home), and the number of participants in every weekly contest has been steadily rising. Compared with when I had just returned to China, it has already doubled. My rating had been falling for about a month, and this week it finally rose again, to 2187, returning to its highest point.

1403. Minimum Subsequence in Non-Increasing Order

This Monday I joined a LeetCode daily check-in and weekly contest group. It publishes rankings every week, and the bottom-ranked person sends a red packet; every day there is a designated problem to solve, and if you miss two consecutive days you also send a red packet. It is extremely intense and exciting. Contest leaderboard.
This was my first contest since joining the group. Because the fourth problem was too hard, only around one hundred people solved it in total. In the group, only five people got AC.

1394. Find Lucky Integer in an Array

1385. Find the Distance Value Between Two Arrays

Sort arr2 first. Then for every element in arr1, use binary search to determine whether arr2 contains a value within distance d.

Since LeetCode updated its rating algorithm, my rating reached its peak and has been dropping ever since. But that is also because I am not good enough; every contest I rank several hundred places down, and occasionally over a thousand.

1389. Create Target Array in the Given Order

Kick Start has changed a little in the new year:

1. Whether all test results are correct is now returned immediately. Previously, large dataset results could only be seen after the contest. This is effectively a difficulty reduction and reduces the cost of mistakes for contestants. In the past, one small mistake meant losing the score for the large dataset. Now it is more like adding a time penalty.
2. The number of problems changed from 3 to 4, with the time unchanged, adding one easier problem for points.

Rank 570. Because everyone got 100 points, the final comparison was all about time. Since the contest was from 12:00 to 15:00, I spent half an hour in the middle eating lunch. Also, none of the problems were accepted on the first try; I debugged all of them with printf, which took quite a bit of time. The fastest experts finished in 20 minutes.

First Round

time: 2020-03-20 16:29:48

Last Friday I took the written test on Nowcoder. The questions were not hard and were divided into computer science fundamentals, algorithms, and system design.
For computer science fundamentals, thanks to serious undergraduate study, there was no problem. The algorithm part was also around LeetCode Medium difficulty and I got AC quickly.
System design, however, stumped me. I am not good at it and had not prepared for it. The task was to design a MOBA game’s matchmaking mechanism, including solo and team queue. I had never thought about it before and just wrote something randomly.
Yesterday I received a call saying I had passed the written test, and they scheduled a phone interview for 2:30 this afternoon.

Since LeetCode updated the weekly contest rating algorithm, the result shocked me. My rating directly rose to 2171, with global rank 608/81184 and 53 contests completed. I remember that last week I was still hoping to break 2000 in the next few weeks, since I was already 1990+. The updated algorithm shows that I had already reached 2000 last August.

This Sunday I went back to the village to visit my grandmother. Because of the pandemic, the family had not been able to get together for a while. Today, at long last, almost everyone was there. I also joined the weekly contest from my hometown. Because the environment was not suitable for thinking, the result was only so-so.